龙舌草果实和种子及其种苗发育形态学研究

采用形态观察和GMA切片相结合的方法,对龙舌草果实、种子及种苗发育的形态结构进行解剖学观察研究,探讨龙舌草个体发育中表现出的与水生环境相适应的结构特征.结果显示:(1)龙舌草由佛焰苞包被的果实通常由6心皮构成,心皮边缘不完全愈合,层片状胎座,水面形成的幼嫩果实被果柄拉入水中发育成熟;种子具毛,萌发时苗端先于根端发育,在胚根分化之前先出现单细胞的下胚轴毛,随后胚根发育为初生根,并在真叶的节处发育出不定根;果皮和叶肉内的维管束仅由少数细胞构成,且细胞分化不明显,有发达的通气道;叶表皮无角质层,细胞外凸,叶肉细胞数量少;表明龙舌草的结构特征与水生环境相适应.(2)研究还发现,龙舌草的种子无胚乳,下胚轴贮存种苗发育需要的大量淀粉粒,以及初生根和不定根均有根毛的结构,且与泽泻科的慈菇和泽泻的结构一致,证明水鳖科与泽泻科具有较近的亲缘关系.

Morphological Study of Fruit,Seed and Seedling Development of Ottelia alismoides (Hydrocharitaceae)

The morphological and anatomical features of fruit,seed and seedling development of Ottelia alismoides were observed in the paper,using the morphological observation and GMA sections and inquire into the structures adapted to the water environment in the ontogenetic development of O.alismoides.The results showed:(1)The O.alismoides fruit enveloped by spathe usually have six carpels and their edges do not connect each other completely in the center of fruit and laminal placentation.The young fruit developed above the water was pulled by the carpopodium into water to mature.The seed is with hairs and its shoot apex develops before root apex.The hypocotyl develops unicellular hairs before the radicle differentiates,and then the radicle develops into primary root and the adventitious root formed in the leaf node.The pericarp and mesophyll are vascular bundles composed of a few cells and well-developed air cananls.The epidermal cells of the leaf have no cuticle and their outer walls are bulging and mesophyll is with less cells.All these features of the species are adapted to the water environment.(2)The authors observed that some features of the species (i.e.,seed has no endosperm;the starch grains are rich in hypocotyl,which offer the nutrient for its development;both primary and adventitious roots have root hairs) could be also found in Sagittaria sagittifolia and Alisma plantago-aquatica of Alismataceae.The study showed the close relationship between two families Hydrocharitaceae and Alismataceae.